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SōLIS SO-8000SōLIS

SōLIS, an audio brand that has been around for four decades, is constantly evolving. Many of its current offerings pair with Google Home and Chromecast devices and it made a nice showing at CES with some very marketable home audio devices. When presented with the SōLIS SO-7500, an amplifier that uses vacuum tubes it was clear those 40 years of experience in the industry have been put to good use. The SO-7500 toes the line between nostalgia and cutting-edge audio, but did not fail to impress on both an aesthetic and auditory level.

The SO-7500 (and its slightly more expensive big brother SōLIS SO-8000) immediately stands out as a very unique audio device. It has vacuum tubes. Vacuum tubes haven't been used widely since the invention of transistors. So it's important to recognize the significance of these besides just nostalgia or aesthetic. The general thought and advertising perspective on vacuum tubes is that they help the amplifier deliver a smooth and detailed sound that raises the tiny hairs on the insides of audiophiles' ears. There is a warmth to music when pushed through the vacuum tubes on the SO-7500, as well as a literal warmth as vacuum tubes literally heat up and visually glow.

Before getting into the specifics of the amplifier, we should hop into the Wayback machine and digest a quick history lesson on vacuum tubes. You can either Google vacuum tubes or in my case, consult the nearest retired electrical/mechanical engineer who literally at one point in his education took a class on amplifier technology. The short of it is that vacuum tubes are a way to convey energy from one side of the circuit to the other, from an anode to a cathode. When you apply energy from one side, the signal is passed to the other side, where it can be amplified. Vacuum tubes are very energy intensive, use a lot of power and are subject to noise (hum) when a tube is going bad. The noise in the actual vacuum tube can't be amplified and at one point in history, that was a drawback to vacuum tubes and let to advances in audio technology that allowed full amplification.

The major advancement in audio technology was when transistors came out in 1957. Transistors basically swept vacuum tubes out of standard audio production, save for use on home television sets. For their place in the process, vacuum tubes handle the final audio output. The power output on the SōLIS SO-7500 only kicks a max of 12W RMS, as these size vacuum tubes are generally limited in their power output to speakers. For reference, typical amplifiers with modern transistors are capable of pushing out near 100W with compatible speakers.

The SōLIS SO-7500 has Bluetooth v4.0 with aptX™, as well as two RCA audio inputs. So I started by listening to a lossless FLAC download of the Black Panther soundtrack (which is awesome, thanks, Kendrick) through Bluetooth. Then I switched to RCA. Then I switched back to Bluetooth. I pretty much did this for about twenty different songs from about 20 different artists. The point here is to see if there are any discernible differences in the sound output based on the audio input. Both inputs delivered crisp, clear lows that had a deepness that bumped the entire house.

I can say this, with a physical volume control on the unit, the initial volume is usually much louder through Bluetooth. Once I normalized that, Bluetooth still tended to present a bit louder on the amplifier. Every level seems to be pumped up, versus plugging in through RCA which provides a bit more leveling. However, when it came to audio fidelity, as I use mostly FLAC files, this was probably the best Bluetooth output I've ever encountered. That's not saying too much, as many Bluetooth speakers (with no amplifier) are generally terrible.

A strange thing happened though, I was actually comfortable enough with the sound through Bluetooth that I continued using the amplifier wirelessly instead of plugging anything in. My history with having any level of confidence in Bluetooth is sketchy at best, so this action says a lot about the quality of the SO-7500. When playing the Sufjan Stevens song "You Are the Blood", a song with plenty of intricate detail and shifting tones, I noticed the precise sound of the SO-7500, picking up the minute details in the music.

The HiFi 2-way bass reflex speakers each hold a woofer and a tweeter, but are not magnetically shielded so keep them away from your television. The speakers are not wireless, connected via banana cables to the amplifier. This is good news, because wireless speakers with a vacuum tube amplifier would just be careless and would negate the smoothing out that the vacuum tubes provide.

It's not that the vacuum tubes deliver an antique sound or anything, but they do help level out the mediums in the music to deliver a cleaner field of sound that is very direct. With garage rock such as The Regrettes or the raggedly beautiful raps of K.Flay, the SO-7500 keeps everything in front of you and never pushes out any distortion.

The two 12AX7 vacuum tubes themselves, the obvious selling point of this amplifier, are slated for 5000 hours of life. After that, they are replaceable for about $20 each. You'll get some hum in the music that you can't seem to explain when one of the tubes is starting to go bad. The SO-7500 came with little white butler gloves for handling, though I haven't used them because getting fingerprints on the amplifier is inevitable with physical buttons and no remote. The tiny gloves do speak to the upper-crust affordability of the unit though, destined to be a functional audio trophy in your entertainment center that combines the past and present of high-quality amplifiers. This is the type of amplifier you purchase when you tend to start every music conversation by telling people what sounds better on vinyl.

So what you get with the SōLIS SO-7500 is a little bit of the past mixed in with the latest in current audio technology. The vacuum Tube/Solid State hybrid amplifier really packs a full stereo punch, without having to rely on maximum wattage or giant speakers. It's got a small footprint and is very unique in both function and aesthetic. This is a stereo amplifier for people who not only truly enjoy listening to music, but those who like to argue that outdated technologies can still be adapted to modern form without losing that argument when it comes time to prove it.

Author Bio: Writing about consumer technology, social media and the deep layers of psychological torture endured by all of it. The world is changing, but that doesn't mean we can't be cynical about it. It's not all sunshine and roses in Silicon Valley. It's self loathing, p...